1. Field of the Invention
This invention relates to semiconductor packages and, more particularly, to a semiconductor package comprising an optically transmissive portion, which separately encapsulates a pair of optoelectronic devices, and an optically opaque portion, which encapsulates the optically transmissive portion to optically isolate the pair of optoelectronic devices.
2. Description of the Related Art
The following descriptions and examples are not admitted to be prior art by virtue of their inclusion within this section.
Optoelectronic devices are becoming increasingly common in automotive, consumer, medical, computer, and telecommunication applications due, in part, to the advantages of optical versus electrical signal transmission. For example, optoelectronic technologies have contributed significant advancements to the telecommunications industry by providing higher data rate and bandwidth capabilities than earlier wire-based technologies. Optoelectronic technologies also demonstrate lower electromagnetic interference (“EMI”) sensitivity and emissions, lower loss interconnections and lower susceptibility to distance related parasitics.
Optoelectronic interconnects relay electronic signals from one location to another using light as a carrier frequency for the signal transmission. Systems employing optoelectronic interconnects are generally composed of a number of building blocks, including optical sources (i.e., “transmitters” or “emitters,” such as light-emitting diodes (LEDs), lasers or photodiodes), transmitter circuitry (e.g., a driver circuit), optical transmission media (e.g., free-space, optical fibers or waveguides), optical detectors (i.e., “receivers” or “photodetectors,” such as PIN diodes) and receiver circuitry (e.g., amplifier or decision circuits). Though many high-performance optoelectronic interconnects have been developed for use within the telecommunications industry, they are not typically suitable for many applications (e.g., consumer-electronics) because of packaging and driver requirements, space needs, heat-dissipation problems, or cost.
Packaging requirements, in particular, play a dominant role in determining the suitability of optoelectronic interconnects within consumer-related applications. For example, an active optical device (e.g., an emitter or photodetector) may be attached to a mount in alignment with a package support member (e.g., a substrate or leadframe). The package support member may include a spherical lensing element for coupling the optical device to an optical fiber arranged above a sensing surface of the optical device. The arrangement of the mounted optical device, the package support member and the lens is generally referred to as an optical subassembly, or OSA. In some cases, the electronic circuitry required for operating the optical device may be separately assembled and coupled to the OSA by conventional means (typically by electrical leads). The supporting electronic circuitry may then be enclosed within a housing, which is separate from an enclosure surrounding the OSA, with only the leads of the support circuitry exposed for connecting to the OSA.
Packaging optical devices and support circuitry within separate packages may be beneficial in some cases. For example, separate package designs provide the ability to interchange the support circuitry required for different electronic signals, such as TTL or ECL signals. Unfortunately, a major disadvantage of separate package designs is the overall size of the resultant package. In particular, the amount of space required to accommodate separate optical and electronic packages is significant. However, the cost involved in making two separate packages is even more significant—especially so in the cost-conscious consumer electronics market. Not only must each package be separately manufactured and maintained, but having two packages might require the optical package not maintain a power supply as would be the case in the electronic package. If the circuitry within the electronic package is defective, the optical package absent a power supply cannot bypass operation of its associated, defective electronic circuitry.
In an effort to overcome the above-mentioned problems, package designs have evolved to combine optical devices and support circuitry within a single package. These single package designs have attempted to minimize the space consumption and electrical parasitics plagued by separate package designs. In general, single package designs may include a package support member (e.g., a substrate or leadframe) upon, or within which, the optical and electronic components are coupled. One or more optical receptacles may be attached to the package support member for receiving one or more optical fiber connectors. In some cases, a lensing element may be included within the package support member or within the optical receptacles to provide optical coupling between the optical device and the optical fiber. Alternatively, the optical fiber may be a “lensed fiber,” and may include a lensing element at one end thereof. Subsequently, portions of the package support member and the optical receptacles may be enclosed within a housing to provide structural rigidity to the semiconductor package. In this manner, signal transmission may occur successfully if the optical receptacles are precisely aligned to the optical devices within the package.
Unfortunately, conventional single package designs suffer from several disadvantages. For example, fabrication problems may exist with respect to mating the various parts of the packaged device (i.e., the housing, the package support member and the optical receptacles). Conventional means of attaching the various parts have included a solder process and a temperature cured epoxy process. These processes require relatively high curing temperatures, and thus, often cause significant thermal expansion within package parts fabricated from thermally conductive materials (e.g., ceramic substrates, metal lead frames, metal housings, etc.). As such, misalignment between an optical receptacle (and thus, an optical fiber) and an optical device may result due to thermal expansion and contraction of the various parts during the high temperature curing/adhesion process and subsequent cooling process.
In any case, securing an optical receptacle to the package typically involves an “active” alignment process. In other words, the alignment of one end of an optical fiber may be adjusted until an optical device detects light emitted from an optical source arranged at an opposite end of the fiber. Unfortunately, active alignment is often time consuming, inefficient and unacceptably expensive for use in manufacturing computer interconnects. For example, an unnecessary number of manufacturing steps is required to separately fabricate and assemble the various parts of the packaged device; these additional steps tend to increase manufacturing costs.
Therefore, a need exists for a fiber-based optoelectronic package, which simplifies current packaging techniques by reducing the number of manufacturing steps, in addition to providing passive alignment between the optical receptacles and optical devices. The cost of manufacturing such a package would be significantly reduced compared to the cost of manufacturing conventional dual optical/electronic packages or packages having receptacles coupled to the package housing.